共查询到20条相似文献,搜索用时 31 毫秒
1.
A novel approach for the suppression of the parallel-plate waveguide (PPW) noise in high-speed printed circuit boards is presented. In this approach, one of the two conductors forming the PPW is replaced by an electromagnetic bandgap (EBG) surface. The main advantage of the proposed approach over the commonly practiced methods is the omnidirectional noise suppression it provides. For this purpose, two EBG structures are initially designed by utilizing an approximate circuit model. Subsequently, the corresponding band structures are characterized by analytical solutions using the transverse resonance method, as well as full-wave finite-element simulations. The designed EBG surfaces were fabricated and employed in a number of PPW test boards. The corresponding frequency-domain measurements exhibited bandgaps of approximately 2.21 and 3.35 GHz in the frequency range below 6 GHz. More importantly, suppression of the PPW noise by 53% was achieved based on time-domain reflectometry experiments, while maintaining the signal transmission quality within the required specifications for common signaling standards. 相似文献
2.
Chen-Chia Wang Trivedi S.B. Feng Jin Khurgin J. Temple D. Hommerich U. Gad E. Fow-Sen Choa Yu-Sung Wu Corder A. 《Lightwave Technology, Journal of》2001,19(5):666-672
A new coherent optical detection technique employing coherent frequency-domain reflectometry and a novel optical frequency sensor is demonstrated for high-precision optical path-length measurements. Using pulsed laser sources, an improvement of more than two orders of magnitude in spatial resolution over conventional optical coherent frequency domain reflectometry techniques is demonstrated. Varying degrees of spatial resolution ranging from several centimeters to a few hundred nanometers are achieved. High-precision distance measurement with long baseline is also presented 相似文献
3.
The characteristics of fading noise in Rayleigh backscattering measurements made with coherent lightwaves such as in coherent-OTDR (optical time-domain reflectometry) and coherent-OFDR (optical frequency-domain reflectometry) are studied. The effects of frequency shift averaging on fading noise reduction are clarified theoretically, and the relationships between measurement accuracy and other parameters, such as spatial resolution and frequency variation range are derived. The calculated results of loss measurement accuracy are in good agreement with experimental data. The formula can also be applied to low-coherence interferometric OTDR 相似文献
4.
Co-planar lines on silicon substrates with and without slow-wave effect are characterized using time-domain reflectometry (TDR) and vector network analyzer (VNA) measurements, and simulated using a proposed nonphysical resistance-inductance-conductance-capacitance (RLGC) model. The silicon co-planar lines are characterized based on comparison to package transmission lines. Co-planar silicon lines without slow-wave mode are modeled in the same way as package transmission lines, but co-planar lines with slow-wave mode are modeled in a different way from package transmission lines. Hence, a nonphysical RLGC model including slow-wave mode is proposed along with the extraction method from VNA measurements. Simulation results correlate well with time- and frequency-domain measurements for the co-planar silicon lines. 相似文献
5.
Shalibeik H. Behrends A. Kozak M. M. Kowalsky W. Caspary R. 《Photonics Technology Letters, IEEE》2007,19(4):188-190
For thulium-doped fiber amplifier (TDFA) design, knowledge of the gain distribution within the active fiber is of great value. For the first time, the distributed gain along highly thulium-doped fibers was measured with high-resolution reflectometry. The technique of coherent optical frequency-domain reflectometry is a nondestructive and noninvasive method well matched to this task due to its dynamic range, spatial resolution, and measurement range. Using thulium-doped fibers with different Tm3+-dopant concentrations, we show precise measurements of Rayleigh backscattering levels for obtaining the optimum gain-length ratio for S-band TDFA pumped by 1050-nm laser diodes 相似文献
6.
A class of frequency-domain adaptive approaches to blind multichannel identification 总被引:3,自引:0,他引:3
We extend our previous studies on adaptive blind channel identification from the time domain into the frequency domain. A class of frequency-domain adaptive approaches, including the multichannel frequency-domain LMS (MCFLMS) and constrained/unconstrained normalized multichannel frequency-domain LMS (NMCFLMS) algorithms, are proposed. By utilizing the fast Fourier transform (FFT) and overlap-save techniques, the convolution and correlation operations that are computationally intensive when performed by the time-domain multichannel LMS (MCLMS) or multichannel Newton (MCN) methods are efficiently implemented in the frequency domain, and the MCFLMS is rigorously derived. In order to achieve independent and uniform convergence for each filter coefficient and, therefore, accelerate the overall convergence, the coefficient updates are properly normalized at each iteration, and the NMCFLMS algorithms are developed. Simulations show that the frequency-domain adaptive approaches perform as well as or better than their time-domain counterparts and the cross-relation (CR) batch method in most practical cases. It is remarkable that for a three-channel acoustic system with long impulse responses (256 taps in each channel) excited by a male speech signal, only the proposed NMCFLMS algorithm succeeds in determining a reasonably accurate channel estimate, which is good enough for applications such as time delay estimation. 相似文献
7.
针对相位敏感光时域反射计(Φ-OTDR)信号处理复杂、计算量大、实时性要求高的特点,提出一种基于现场可编程门阵列(FPGA)异构加速计算技术的Φ-OTDR实时信号处理系统。对外差探测式Φ-OTDR信号处理流程进行分析与分解,提出基于FPGA的滑动窗数据帧分割、多通道并行快速傅里叶变换(FFT)计算、频域滤波、短时能量求和等一系列加速计算方法。该系统最终实现在40 km光纤传感距离、2 kHz重复频率与1 m采样间隔下的长时间、实时扰动信号解调与显示,并且具有80%的帧重叠率。该FPGA系统作为异构加速器,能够减轻计算机数据处理压力,保证传感系统高重复频率下的运算实时性,为系统可靠性和稳定性提供了有效保障。 相似文献
8.
《IEEE transactions on circuits and systems. I, Regular papers》2009,56(11):2439-2448
9.
This paper is concerned with detecting the period of cyclic object motion in a short video or sequence with a limited number of frames. This problem can be studied with either frequency-domain methods or time-domain methods. A frequency-domain method is fundamentally limited in terms of frequency resolution—especially with a small number of frames—and its ability to handle a periodic impulsive or spiky signal. Existing time-domain methods are primarily based on an analysis of the autocorrelation function of a signal and can be sensitive to noise in the signal. In this paper, we offer an alternative time-domain method. Rather than using autocorrelation as the basis, our proposed method uses peak analysis. Specifically, after computing the similarity between a reference image and those in the sequence, our algorithm applies one of two period detection procedures—one based on clustering and the other on watershed to analyze the peaks of the similarity time series—in estimating the period of object motion embedded in the similarity function. Video sequences from three different applications are used to establish the feasibility of our proposed algorithm and its superiority to competing algorithms. 相似文献
10.
Ortega J.M.M. Esteve M.P. Payan M.B. Exposito A.G. Franquelo L.G. 《Power Electronics, IEEE Transactions on》2005,20(2):446-456
This paper focuses on the steady-state response of existing methods for computing the reference current of active power filters. For each class of methods, the main source of discrepancy between the load harmonic current and the computed reference current is identified and the frequency spectrum of the resulting error is analytically determined. Although this topic has been partially addressed in previous publications, the proposed frequency-domain approach provides valuable qualitative information about how the errors are produced and distributed, which is masked when the analysis is carried out in the time domain. First, the frequency-domain formulation is separately presented for each method. Then, a comparison of the resulting errors is performed on a case study. Finally, some experimental results are given to validate the proposed frequency-domain analysis. 相似文献
11.
We propose and demonstrate a novel linearizing method of optical frequency-sweep of a laser diode for frequency-modulated continuous-wave (FMCW) reflectometry. In order to linearly sweep the optical frequency, we adopt a reference interferometer and an electric phase comparator. The interference beat signal of the reference interferometer is phase-compared with an external reference rectangular signal having a fixed frequency near the interference beat signal frequency by a lock-in amplifier. The error signal from the lock-in amplifier is fed back to the modulating signal of the injection current of the laser. Thus, a phase-locked loop composed of optical and electric circuits can be established, and the beat signal frequency is locked to the frequency of the reference signal. The optical frequency of the laser diode is, therefore, excellently linearly swept in time. In order to experimentally confirm the linearity of the proposed method, we apply this frequency-swept laser diode to the FMCW reflectometry. Resultingly, the improvement of the linearity is estimated to be about 10 dB. And the theoretically limited spatial resolution of the FMCW reflectometry is achieved. The backscattered light in optical waveguide devices is measured by the FMCW reflectometry using the proposed light source, and the propagation loss of a single-mode glass waveguide is successfully evaluated 相似文献
12.
Yuriy V. Zakharov Tim C. Tozer David A. J. Pearce 《Signal Processing, IEEE Transactions on》2007,55(2):585-593
Low-complexity delayless acoustic echo cancellation techniques based on frequency-domain spline-identification are proposed and investigated. Two methods of approximation of the acoustic frequency response, both using B-splines, are considered: the optimal-spline method and the local-spline method. The optimal-spline method seeks the solution of a least squares problem. The most computationally demanding part of the method, solution of the normal equations, is implemented by using the low-complexity dichotomous coordinate descent algorithm. The local-spline method avoids solving the normal equations, enabling further simplification; this is at the expense of a slight degradation in the cancellation performance. A novel efficient double-talk detector is also proposed, being an inherent feature of the frequency-domain identification. Open-loop and closed-loop identification schemes with cubic splines are studied by simulation and compared with the fast affine projection (FAP) algorithm. The proposed techniques provide cancellation performance better than that of the FAP algorithm, especially in double-talk and noisy environments, with a lower complexity 相似文献
13.
《Vehicular Technology, IEEE Transactions on》2009,58(9):4903-4908
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16.
von der Weid J.P. Passy R. Huttner B. Guinard O. Gisin N. 《Photonics Technology Letters, IEEE》1998,10(7):949-951
For the first time, the distributed gain along erbium-doped fibers was measured with high-resolution reflectometry. The coherent optical frequency-domain reflectometry detection technique intrinsically filters amplified spontaneous emission, allowing precise measurements of Rayleigh backscattering levels and nondestructive determination of the optimum length of the doped fiber for different pump and probe conditions 相似文献
17.
Pin-Hsun Lin Tzi-Dar Chiueh 《Communications Letters, IEEE》2004,8(6):339-341
In this letter, a frequency-domain despreading method for the cyclic-prefix code-division multiple-access (CP-CDMA) system is introduced. Using the orthogonality transformation property of the discrete Fourier transform (DFT), we can despread the received CP-CDMA signals in the frequency domain. Moreover, we propose an efficient architecture for the proposed frequency-domain despreader. Comparison with the conventional time-domain despreading approach shows that the proposed architecture can save a large amount of computation. The proposed scheme is therefore suitable for efficient implementation of CP-CDMA receivers that adopt frequency-domain equalization and despreading. 相似文献
18.
A refractometer for liquids, based on optical frequency-domain reflectometry, is described which uses a simple fibre probe with minimal contact area with the test liquid. The sensitivity is much better than in earlier reported fibre refractometers. 相似文献
19.
Fabrication methods for low drive voltage and broad-band LiNbO3 waveguide directional coupler optical modulator are described. Optical waveguides were prepared by conventionaly Ti in-diffusion into LiNbO3 c -cut plate. To obtain wide-band frequency response, traveling wave electrodes were used. Electrode characteristic impedance measured by time domain reflectometry method coincided well with the calculated value by conformal mapping. Measured electrode conductor losses followed square root of frequency. To reduce electrode conductor losses, asymmetric and 3-μm thick Al electrodes were used. Directional coupler optical modulator frequency response was analyzed, using the phase difference average value along the propagation directions. Calculated value by this method coincided well with measured value obtained by a swept frequency technique. The characteristics of this modulator at the 1.317-μm wavelength are as follows: 100 percent modulation voltage is 4 V, extinction ratio is 17 dB, optical insertion loss is 5.4 dB, 3-dB bandwidth is 3.6 GHz, and rise time is about 400ps. 相似文献